A prior art automatic steering method using such kind of an automatic steering system is known, for example, from Patent Document No. 1 listed below. With this method, automatic steering is conducted for an agricultural vehicle having automatic maneuvering functionality. The heading direction of the vehicle is detected by means of a heading direction sensor, such as a geomagnetic azimuth sensor or a gyroscope, and any deviation of the actual heading direction from a desired heading direction is determined in order to control the steering mechanism of the vehicle such that the vehicle may keep the desired heading direction.
Patent Document No. 2 listed below describes an automatic rice-planting vehicle having a direction sensor, such as a geomagnetic azimuth sensor or a gyroscope. During a training running operation, the rice-planting vehicle collects data indicating a desired heading direction. When operated to run by automatic maneuvering, the vehicle is controlled by an automatic steering system such that it may keep the desired heading direction indicated by the collected data. In addition, the desired heading direction is updated by collecting new direction data and effecting an averaging operation to them. When used for work, the rice-planting vehicle usually runs along a serpentine pattern of a running path having parallel, straight sections. The process of updating the desired heading direction improves the parallelism of the parallel, straight sections of the running path.
Patent Document No. 3 listed below describes a driverless maneuvering of a tractor. The position and heading direction of the tractor are detected in real-time manner by means of a fiber optic gyroscope and a geomagnetic azimuth sensor. The tractor is intended to run along a predetermined running path, by which desired positions and heading directions of the tractor are defined. When the tractor is steered by real-time steering control, any deviation of the actual position and heading direction of the tractor from the corresponding desired position and heading direction is continuously determined and the desired steering angle is so determined as to eliminate such deviation.